Liquid-pressure rotating device

ABSTRACT

A cylinder block including plurality of piston chambers formed at intervals in circumferential direction; plurality of pistons fitted in respective piston chambers movable in expanding and contracting directions to reciprocate in the expanding and contracting directions; a valve plate in contact with the cylinder block rear end surface and including first and second ports communicating with piston chambers. A portion of each ports is close to a top dead center switching land formed between first and second ports as a portion having a narrow opening width in a rotation radial direction of the cylinder block. An auxiliary port is formed at the valve plate switching land. Auxiliary port pressure is maintained lower than pressure of a side port that is the first or second port. When the piston chamber lacks communication with the side port (first or second port), the piston chamber and auxiliary port communicate with each other.

TECHNICAL FIELD

The present invention relates to a liquid-pressure rotating device thatcan be used as a liquid-pressure motor or a liquid-pressure pump.

BACKGROUND ART

One example of a valve plate provided in a conventional liquid-pressuremotor is shown in FIG. 9 (see PTL 1, for example). Main ports 2 and 3are formed on a valve plate 1. Each of the main ports 2 and 3 is formedin a circular-arc shape extending along a route of a rotational movementof a cylinder port (not shown), and an opening width of each of the mainports 2 and 3 in a radial direction is a constant size W4.

Currently, high-pressure operating oil in the cylinder port (pistonchamber) closed by the valve plate 1 is leaking through a sealed regionbetween the valve plate 1 and a cylinder block, and a reduction in thisleak amount is required.

CITATION LIST Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 45-39126

SUMMARY OF INVENTION

Technical Problem

It may be considered that to reduce the amount of operating oil leakingthrough the main ports, the opening width W4 of each of the main ports 2and 3 is reduced. However, in this case, pressure loss of the operatingoil flowing through each of the main ports 2 and 3 increases, and thiscauses a problem that mechanical efficiency of the liquid-pressure motordecreases.

The present invention was made to solve the above problem, and an objectof the present invention is to provide a liquid-pressure rotating devicecapable of: reducing the amount of high-pressure operating oil leakingfrom a first or second port through a sealed region between a cylinderblock and a valve plate; and suppressing an increase in pressure loss ofoperating oil flowing through each of the first and second ports.

Solution to Problem

A liquid-pressure rotating device according to the present inventionincludes: a cylinder block provided rotatably and including a pluralityof piston chambers formed at intervals in a circumferential direction; aplurality of pistons fitted in the respective piston chambers so as tobe movable in an expanding direction and a contracting direction andconfigured to reciprocate in the expanding direction and the contractingdirection; and a valve plate provided in contact with the cylinder blockand including a first port, a second port, and a switching land formedbetween the first port and the second port, the first and second portscommunicating with the piston chambers, wherein: a portion of at leastone of the first and second ports of the valve plate which portion islocated close to the switching land is formed as a narrow portion havinga narrow opening width in a radial direction; an auxiliary port isformed at the switching land of the valve plate; pressure of theauxiliary port is maintained lower than pressure of a high pressure sideport that is any one of the first and second ports; and when the pistonchamber does not communicate with the high pressure side port that isthe first or second port, the piston chamber and the auxiliary portcommunicate with each other.

In the liquid-pressure rotating device according to the presentinvention, the portions of the first and second ports which portions arelocated close to the switching land are formed as the narrow portionseach having the narrow opening width in the radial direction of therotation of the cylinder block. Therefore, a seal area between thecylinder block and the valve plate can be increased by the narrowportions. The amount of high-pressure operating liquid leaking from thepiston chamber through the first or second port can be reduced by asealed region corresponding to the increased seal area.

The flow rate (the change amount of the volume of the piston chamber perunit rotation) of the operating liquid flowing through the portion ofeach of the first and second ports which portion is located close to theswitching land is lower than the flow rate (the change amount of thevolume of the piston chamber per unit rotation) of the operating liquidflowing through a portion of each of the first and second ports whichportion is located far from the switching land. Therefore, even thoughthe narrow portions are formed at the above portions, the pressure lossbased on the flow of the operating liquid can be prevented fromincreasing to such a degree that the influence of the pressure loss isapparent. The reason why the flow rate of the operating liquid flowingthrough the portion close to the switching land is low is because themovement speed of the piston in the expanding and contracting directionsbecomes slow as the piston gets close to the switching land.

The narrow portions are not formed at the portions of the first andsecond ports which portions are located far from the switching land.Therefore, the pressure loss based on the flow of the operating liquidflowing through the far portions other than the narrow portions does notincrease.

Further, when the piston chamber performs a rotational movement at thedead center and the vicinity of the dead center without communicatingwith the high pressure side port that is the first or second port, thehigh-pressure operating liquid in the piston chamber can be dischargedthrough the auxiliary port. To be specific, the pressure of theoperating liquid in the piston chamber at the dead center or thevicinity of the dead center which pressure contributes little to therotation of the cylinder block and generates high resistance forceagainst the rotation can be reduced, and the mechanical efficiency ofthe liquid-pressure rotating device can be improved.

The liquid-pressure rotating device according to the present inventionmay be configured such that the narrow portion is formed in an anglerange from a position of a dead center to a position of not more than45° in the circumferential direction.

By forming the narrow portions as above, the amount of high-pressureoperating liquid leaking from the first or second port through thesealed region between the cylinder block and the valve plate can beeffectively reduced, and the increase in the pressure loss by the flowof the operating liquid at the narrow portions can be effectivelysuppressed. To be specific, in a case where the rotation angle of thepiston when the piston is located at the dead center is regarded as 0°,and the rotation angle of the piston which has moved in accordance withthe rotation of the cylinder block is represented by θ, the movementspeed of the piston in the expanding and contracting directions can becalculated as a value which changes based on a sine function in which avertical axis denotes the movement speed of the piston in the expandingand contracting directions, and a horizontal axis denotes the rotationangle of the piston. The movement speed of the piston at the angleposition where the rotation angle θ is 45° is about 70% of the maximummovement speed (the movement speed of the piston becomes the maximummovement speed when the piston is located at the angle position wherethe rotation angle θ is 90°. The flow rate of the operating liquid basedon the movement of the piston also becomes about 70% of the maximum flowrate. Therefore, the opening width of the narrow portion in the radialdirection can be set to about 70% of the opening width of the portionother than the narrow portion of each of the first and second ports, andthe sealed region having an appropriate width can be formed.

The liquid-pressure rotating device according to the present inventionmay be configured such that: openings of the piston chambers whichopenings face the valve plate serve as cylinder ports; and the openingwidth of the narrow portion in the radial direction decreases as thenarrow portion extends toward the dead center.

With this, when a bridge portion between the cylinder ports is locatedat the narrow portion by the rotation of the cylinder block, the sealwidth between the cylinder block and the valve plate in thecircumferential direction becomes large. Therefore, the increase in thepressure loss based on the flow of the operating liquid at the narrowportion can be effectively suppressed while reducing the amount ofhigh-pressure operating liquid leaking through between the cylinderblock and the valve plate. To be specific, the flow rate of theoperating liquid in the piston chamber decreases as the piston chambermoves toward the dead center (θ=0°) of the valve plate. Therefore, byreducing the opening width of the narrow portion in the radial directionas the narrow portion extends toward the dead center of the valve plate,the above effects can be obtained.

The liquid-pressure rotating device according to the present inventionmay be configured such that: openings of the piston chambers whichopenings face the valve plate serve as cylinder ports; each of thecylinder ports has a shape including a base portion and a convex portionprojecting from the base portion outward or inward in the radialdirection; the convex portion is formed such that when the pistonchamber communicates with the auxiliary port through the cylinder port,only the convex portion communicates with the auxiliary port; and beforeand after the piston chamber communicates with the auxiliary portthrough the cylinder port, the base portion is located away from theauxiliary port by a sealing portion having a predetermined seal width inthe radial direction.

With this, when the cylinder port performs the rotational movement atthe dead center of the valve plate and the vicinity of the dead center,the base portion of the cylinder port can be located away from theauxiliary port by the sealing portion having the predetermined sealwidth in the radial direction. With this, in a state where the baseportion of the cylinder port at the dead center of the valve plate orthe vicinity of the dead center communicates with the high pressure sideport that is the first or second port, the high-pressure operatingliquid in the piston chamber can be prevented from flowing out throughthe base portion to the auxiliary port. With this, the communicationbetween the base portion and the auxiliary port can be prevented, andthe flow out of the operating liquid to the auxiliary port from aportion other than the convex portion can be prevented. Therefore, thevolume efficiency improves.

The liquid-pressure rotating device according to the present inventionmay be configured such that the seal width is not less than 3 mm.

With this, in a state where the base portion of the cylinder port at thedead center of the valve plate or the vicinity of the dead centercommunicates with the high pressure side port that is the first orsecond port, the base portion is located away from the auxiliary port bythe sealing portion having the seal width of 3 mm or more in the radialdirection. Therefore, it is possible to effectively prevent a case wherethe high-pressure operating liquid in the piston chamber leaks from thesealing portion having the seal width of not less than 3 mm to flow intothe auxiliary port.

Advantageous Effects of Invention

In the liquid-pressure rotating device according to the presentinvention, the portions of the first and second ports which portions arelocated close to the switching land are formed as the narrow portions,so that the amount of high-pressure operating liquid leaking from thefirst or second port through the sealed region between the rear endsurface of the cylinder block and the valve plate can be reduced, andthe increase in the pressure loss of the operating liquid flowingthrough the first and second ports can be suppressed. Thus, the overallefficiency of the liquid-pressure rotating device can be effectivelyimproved.

The above object, other objects, features, and advantages of the presentinvention will be made clear by the following detailed explanation ofpreferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view showing a valve plate of a liquid-pressurerotating device according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the liquid-pressure rotatingdevice according to the embodiment.

FIG. 3 is an enlarged cross-sectional view showing a part of theliquid-pressure rotating device of FIG. 2.

FIG. 4 is an enlarged front view showing an upper half of the valveplate of FIG. 1.

FIG. 5 is an enlarged front view showing a lower half of the valve plateof FIG. 1.

FIG. 6 is a diagram showing a relation between an angle position θ of apiston chamber provided in the liquid-pressure rotating device of FIG. 2and a stroke position of a piston.

FIG. 7 is a diagram showing a relation between the angle position θ ofthe piston chamber provided in the liquid-pressure rotating device ofFIG. 2 and pressure of operating oil in the piston chamber.

FIG. 8A is a front view showing the valve plate of the liquid-pressurerotating device according to another embodiment of the presentinvention. FIG. 8B is an A-A enlarged cross-sectional view showing thevalve plate of FIG. 8A.

FIG. 9 is a front view showing a valve plate of a conventional liquidmotor.

DESCRIPTION OF EMBODIMENTS

Hereinafter, one embodiment of a liquid-pressure rotating deviceaccording to the present invention will be explained in reference toFIGS. 1 to 7. This embodiment will explain an example in which theliquid-pressure rotating device is used as an oil-pressure motor. Itshould be noted that the liquid-pressure rotating device can also beused as an oil-pressure pump.

An oil-pressure motor (liquid-pressure rotating device) 10 is a swashplate type oil-pressure motor configured to convert pressure ofoperating oil (operating liquid) into rotational force to output therotational force. For example, the oil-pressure motor 10 is provided inan industrial machine, a construction machine, or the like and is usedto drive the machine. As shown in FIG. 2, the oil-pressure motor 10includes a valve plate 11, a cylinder block 12, a plurality of pistons13, a plurality of shoes 14, and a swash plate 15, and these componentsare accommodated in a casing 16 included in the oil-pressure motor 10.The casing 16 includes a casing main body 16 a, a front cover 16 b, anda valve casing 16 c.

The oil-pressure motor 10 further includes a rotating shaft 17. A firstend portion 17 a of the rotating shaft 17 is supported by the frontcover 16 b through a first bearing 19 so as to partially project fromthe front cover 16 b and be rotatable around a rotation axis L10 thatcoincides with an axis of the rotating shaft 17. Further, a second endportion 17 b of the rotating shaft 17 is supported by the valve casing16 c through a second bearing 20 so as to be rotatable around therotation axis L10.

As shown in FIGS. 1 and 2, the valve plate 11 has a substantiallycircular plate shape and is provided to be fixed to the valve casing 16c in a state where the rotating shaft 17 is inserted through the valveplate 11. Two supply/discharge ports 21 and 22 (first and second ports)and two auxiliary ports 23 and 24 are formed on the valve plate 11. Inthe valve plate 11 shown in FIG. 1, the supply/discharge ports 21 and 22are formed bilaterally symmetrically, and each of the supply/dischargeports 21 and 22 extends in a circumferential direction around therotation axis L10 and is formed in a circular-arc shape. Each of thesupply/discharge ports 21 and 22 includes tapered notches 90 at bothrespective circumferential-direction end portions thereof. Each of thenotches 90 serves as a pressure change suppressing portion configured toreduce a gradient of a change in the pressure of the operating oil in abelow-described piston chamber 27 and is formed so as to be able toreduce: a steep pressure change caused by switching between connectionwith the piston chamber 27 and disconnection from the piston chamber 27;and noise generated by the pressure change.

The upper auxiliary port 23 is provided at a top dead center switchingland formed between one end portion of the supply/discharge port 21 andone end portion of the supply/discharge port 22, and the lower auxiliaryport 24 is provided at a bottom dead center switching land formedbetween the other end portion of the supply/discharge port 21 and theother end portion of the supply/discharge port 22. To facilitateunderstanding, in FIGS. 2 and 3, the position of the supply/dischargeport 21 is shifted in the circumferential direction from an actualposition.

The cylinder block 12 is provided at the rotating shaft 17 such that:the rotating shaft 17 is inserted through a center of the cylinder block12; and the cylinder block 12 and the rotating shaft 17 are preventedfrom rotating relative to each other by, for example, spline. Thus, thecylinder block 12 is provided rotatably around the rotation axis L10. Aplurality of (nine, for example) piston chambers 27 are formed on thecylinder block 12 at substantially regular intervals in thecircumferential direction. Further, cylinder ports 28 communicating withthe respective piston chambers 27 are formed on the cylinder block 12 atsubstantially regular intervals in the circumferential direction. Thepiston chambers 27 are open at an axial rear end portion of the cylinderblock 12 through the cylinder ports 28. A rear end surface 12 a of thecylinder block 12 slidably contacts the valve plate 11, and a sealstructure is realized between the cylinder block 12 and the valve plate11. In accordance with a rotation angle position of the cylinder block12, the cylinder ports 28 are connected to the left supply/dischargeport 21, the right supply/discharge port 22, the upper auxiliary port23, and the lower auxiliary port 24.

Each of the pistons 13 has a substantially columnar shape. Each of thepistons 13 is fitted and accommodated in the piston chamber 27 of thecylinder block 12 so as to realize a sealed state between the piston 13and the piston chamber 27. Each of the pistons 13 forms an oil-pressurechamber 31. Each of the pistons 13 is provided so as to be movable in anexpanding direction and contracting direction along an axis of thepiston 13. The volumes of the oil-pressure chambers 31 change by themovements of the pistons 13. Each of outer surfaces of first endportions 33 of the pistons 13 is formed in a spherical shape, the firstend portions 33 projecting from the piston chambers 27.

Each of the shoes 14 includes a flange portion 35 having a contactsurface 34 which is located at one end portion of the shoe 14 andperpendicular to an axis of the shoe 14. Each of the shoes 14 forms afitting concave space 36 that is open at the other end portion of theshoe 14. An inner surface of the shoe 14 which surface faces the fittingconcave space 36 is formed in a spherical shape. The first end portion33 of the piston 13 is fitted in the fitting concave space 36. The shoe14 is coupled to the piston 13 so as to be rotatable around threeorthogonal axes by using a center of each of the fitting concave space36 and the first end portion 33 as a rotation center.

The swash plate 15 is provided close to a left end portion of thecylinder block 12 shown in FIG. 2 and includes a flat supporting surface37 that receives and supports the contact surfaces of the shoes 14. Theswash plate 15 is provided so as to be tiltable around a tilt axis L11orthogonal to the rotation axis L10. The swash plate 15 is tilted aroundthe tilt axis L11 by a servo mechanism 38 included in the oil-pressuremotor 10. Thus, an angle of the supporting surface 37 with respect tothe rotation axis L10 is changed.

The oil-pressure motor 10 shown in FIG. 2 further includes a retainerguide 40 and a pressing member 41. The retainer guide 40 is provided atthe rotating shaft 17 such that: the rotating shaft 17 is coaxiallyinserted through the retainer guide 40; and the retainer guide 40 andthe rotating shaft 17 are prevented from rotating relative to each otherby, for example, spline. The retainer guide 40 includes a guide surfacethat is spherical about a point on the rotation axis L10, that is, anintersection point of the axes L10 and L11 in the present embodiment.The pressing member 41 is provided so as to be supported by the guidesurface of the retainer guide 40 and rotatable around three orthogonalaxes by using a center of a sphere including the guide surface, that is,the intersection point of the axes L10 and L11 as a rotation center. Thepressing member 41 locks the flange portions 35 of the shoes 14 to pressthe shoes 14 against the supporting surface 37 of the swash plate 15. Inthis state, each of the shoes 14 is allowed to slightly move relative tothe pressing member 41 in directions along the supporting surface 37 ofthe swash plate 15 and a rotational direction whose rotation center isthe intersection point of the axes L10 and L11.

In the oil-pressure motor 10, a spring member (not shown) such as acompression coil spring is provided at the cylinder block 12, and springforce of the spring member is transferred to the retainer guide 40. Withthis, the retainer guide 40 guides and supports the pressing member 41as described above to press the pressing member 41 against the swashplate 15. Then, the pressing member 41 presses the shoes 14 against theswash plate 15. Thus, the shoes 14 are prevented from being separatedfrom and floating from the swash plate 15.

The oil-pressure motor 10 is configured such that when the cylinderblock 12 rotates once, each of the pistons 13 reciprocates once. Areciprocating movement of the piston 13 includes a top dead center and abottom dead center at angle positions corresponding to every 180° whenthe piston 13 performs the rotational movement about the rotation axisL10. Specifically, the top dead center and the bottom dead center arelocated at respective angle positions at each of which a virtual flatsurface including the rotation axis L10 and vertical to the tilt axisL11 and the axis of the piston 13 coincide with each other.

The piston chamber 27 in which the piston 13 at the dead center or thevicinity of the dead center is fitted is connected to the auxiliary port23 or 24 through the cylinder port 28. Specifically, when the pistonchamber 27 is located in an angle range from an angle position when thepiston 13 is located at the top dead center that is the most contractedposition toward each of both sides in the circumferential direction byan angle θ1, the piston chamber 27 is connected to the upper auxiliaryport 23. Further, when the piston chamber 27 is located in an anglerange from an angle position when the piston 13 is located at the bottomdead center that is the most contracted position toward each of bothsides in the circumferential direction by the angle θ1, the pistonchamber 27 is connected to the lower auxiliary port 24. The angle θ1 isset to, for example, about 10°.

On the other hand, the piston chamber 27 in which the piston 13 at aposition other than the dead center and the vicinity of the dead centeris fitted is connected to the supply/discharge port 21 or 22 through thecylinder port 28. Specifically, when the cylinder block 12 is viewedfrom the first end portion 17 a of the rotating shaft 17, and thecylinder block 12 rotates in a counterclockwise direction that is adirection shown by an arrow A1 in FIG. 1, the piston chamber 27 locatedat the angle position where the piston 13 is expanding except for thetop dead center, the vicinity of the top dead center, the bottom deadcenter, and the vicinity of the bottom dead center is connected to thesupply/discharge port 21. Further, when the cylinder block 12 is viewedfrom the first axial end portion 17 a of the rotating shaft 17, and thecylinder block 12 rotates in a clockwise direction that is a directionshown by an arrow A2 in FIG. 1, the piston chamber 27 located at theangle position where the piston 13 is expanding except for one of thedead centers, the vicinity of the one dead center, the other deadcenter, and the vicinity of the other dead center is connected to thesupply/discharge port 22.

Each of an angle range where the piston 13 moves in the expandingdirection except for the dead centers and the vicinities of the deadcenters and an angle range where the piston 13 moves in the contractingdirection except for the dead centers and the vicinities of the deadcenters is represented by {180−(2×θ1)}°. Therefore, each of these angleranges is smaller than 180°. As above, each of the piston chambers 27 isconnected to any one of the ports 21 to 24 in accordance with the angleposition.

As shown in FIG. 2, the valve casing 16 c of the oil-pressure motor 10includes: a supply/discharge passage 51 communicating with thesupply/discharge port 21 of the valve plate 11; and a supply/dischargepassage (not shown) communicating with the supply/discharge port 22 ofthe valve plate 11. These supply/discharge passages communicate with anoil-pressure source, such as a pump, or a tank (both not shown) providedseparately from the oil-pressure motor 10.

As shown in FIG. 1, in the present embodiment, the supply/dischargeports 21 and 22 of the valve plate 11 are formed symmetrically relativeto the rotation axis L10 that is the axis of the valve plate 11, and theauxiliary ports 23 and 24 of the valve plate 11 are formed symmetricallyrelative to the rotation axis L10. Therefore, the oil-pressure motor 10is rotatable in both normal and reverse directions. The operating oil isejected from the oil-pressure source to be supplied through thesupply/discharge passage 51 to the supply/discharge port 21 of theoil-pressure motor 10. Further, the operating oil is discharged from thesupply/discharge port 22 of the oil-pressure motor 10 through thesupply/discharge passage to an outside of the oil-pressure motor 10.With this, the piston in the piston chamber 27 connected to thesupply/discharge port 21 expands. Thus, the cylinder block 12 rotates inthe rotational direction A1, and the rotating shaft 17 also rotates inthe rotational direction A1. For example, the rotation of the rotatingshaft 17 can be output from the first end portion 17 a to drive theother machine or the like in the same direction.

The supply/discharge port 21 serves as a first port to which theoperating oil of high pressure, such as 35 MPa, which can drive theoil-pressure motor 10 is introduced from the oil-pressure source. Thesupply/discharge port 22 serves as a second port from which theoperating oil discharged from the oil-pressure chamber 31 flows out, andthe operating oil is discharged to the outside of the oil-pressure motor10. Each of the auxiliary ports 23 and 24 serves as a third port. Thepressure of the operating oil introduced to each of the auxiliary ports23 and 24 is maintained higher than atmospheric pressure and lower thanthe pressure ejected from the oil-pressure source to thesupply/discharge port 21 that is the high-pressure first port. Forexample, the pressure of the operating oil introduced to the auxiliaryports 23 and 24 is maintained not less than 0.01 MPa and not more than 2MPa.

Further, the operating oil is ejected from the oil-pressure source to besupplied through the supply/discharge passage to the supply/dischargeport 22 of the oil-pressure motor 10. Then, the operating oil isdischarged from the supply/discharge port 21 of the oil-pressure motor10 through the supply/discharge passage 51 to the outside of theoil-pressure motor 10. With this, the piston 13 in the piston chamber 27connected to the supply/discharge port 22 expands. Thus, the cylinderblock 12 rotates in the rotational direction A2 opposite to therotational direction A1, and the rotating shaft 17 also rotates in therotational direction A2. For example, the rotation of the rotating shaft17 can be output from the first end portion 17 a to drive the othermachine or the like in the same direction.

In this case, the supply/discharge port 22 serves as the first port towhich the operating oil of high pressure which can drive theoil-pressure motor 10 is introduced from the oil-pressure source. Thesupply/discharge port 21 serves as the second port from which theoperating oil discharged from the oil-pressure chamber 31 flows out, andthe operating oil is discharged to the outside of the oil-pressure motor10. Further, also in this case, each of the auxiliary ports 23 and 24serves as the third port. The pressure of the operating oil introducedto each of the auxiliary ports 23 and 24 is maintained higher than theatmospheric pressure and lower than the pressure ejected from theoil-pressure source to the supply/discharge port 22 that is thehigh-pressure first port. For example, the pressure of the operating oilintroduced to the auxiliary ports 23 and 24 is maintained not less than0.01 MPa and not more than 2 MPa.

As above, in the oil-pressure motor 10, when the piston 13 is notlocated at the dead center or the vicinity of the dead center and islocated in a range where the piston 13 moves in the expanding direction,the piston chamber 27 communicates with the first port of the valveplate 11, and the high-pressure operating oil is introduced to thepiston chamber 27. Further, when the piston 13 is not located at thedead center or the vicinity of the dead center and is located in a rangewhere the piston 13 moves in the contracting direction, the pistonchamber 27 communicates with the second port of the valve plate 11, andthe low-pressure operating oil can be discharged to a discharge place.Furthermore, the piston chamber 27 located in the angle range where thepiston 13 is located at the dead center or the vicinity of the deadcenter communicates with the auxiliary port 23 or 24 of the valve plate11, and the high-pressure operating oil in this piston chamber 27 can bedischarged through the auxiliary port 23 or 24 and a drain port 137 (seeFIG. 2) to, for example, a drain tank lower in pressure than the pistonchamber 27.

Thus, the cylinder block 12 can be rotated by the pressure of theoperating oil, and the rotation of the cylinder block 12 can be outputfrom the rotating shaft 17. As above, the oil-pressure motor 10 candrive, for example, a device provided separately. Further, the pistonchamber 27 located in the range where the piston 13 is located at thedead center or the vicinity of the dead center is connected to theauxiliary port, and the operating oil can be supplied to or dischargedfrom the piston chamber 27. With this, the smooth movement of the pistonin the vicinity of the dead center can be realized in the expandingdirection and the contracting direction.

FIG. 4 is an enlarged view showing the upper auxiliary port 23 of FIG. 1and its vicinity. An opening of the cylinder port 28 which opening facesthe valve plate 11 is formed in a shape including a base portion 67 anda convex portion 68 projecting from the base portion 67 at least outwardor inward in a radial direction. In the present embodiment, the baseportion 67 has a substantially long cylindrical shape, and each of aninner peripheral edge side 70 and outer peripheral edge side 71 of thebase portion 67 is formed so as to coincide with a virtual cylindricalsurface about the rotation axis L10. The convex portion 68 is formed toproject inward in the radial direction from a circumferential-directionmiddle portion of the base portion 67.

FIG. 6 is a diagram showing a relation between an angle position θ ofthe piston chamber 27 and a stroke position of the piston 13. FIG. 7 isa diagram showing a relation between the angle position θ of the pistonchamber 27 and pressure P of the operating oil in the piston chamber 27.Regarding a horizontal axis in FIGS. 6 and 7, the angle position θ ofthe piston chamber 27 when the piston 13 is located at one of the deadcenters is 0°, and an angle in the rotational direction A1 from theangle position of 0° is shown by 0. In FIG. 6, a vertical axis denotesthe stroke position of the piston 13. The stroke position at one of thedead centers is shown by 0, and the stroke position at the other deadcenter is shown by I. In FIG. 7, a vertical axis denotes the pressure Pof the operating oil in the piston chamber 27. Lowest pressure andhighest pressure while the piston 13 reciprocates once, that is, whilethe piston chamber 27 rotates once are shown by P1 and P2, respectively.

When the angle θ1 is 10° as described above, and the piston chamber 27(i.e., the cylinder port 28) is located in an angle range of more than10° and less than 170° (10<θ<170), the piston chamber 27 (i.e., thecylinder port 28) is connected to the supply/discharge port 21. When thepiston chamber 27 (i.e., the cylinder port 28) is located in an anglerange of more than 190° and less than 350° (190<θ<350), the pistonchamber 27 (i.e., the cylinder port 28) is connected to thesupply/discharge port 22. Further, when the cylinder port 28 is locatedin an angle range of not less than 0° and not more than 10° (0≦θ≦10) oran angle range of not less than 350° and less than 360° (350≦θ<360), thecylinder port 28 is connected to the upper auxiliary port 23. When thecylinder port 28 is located in an angle range of not less than 170° andnot more than 190° (170≦θ≦190), the cylinder port 28 is connected to thelower auxiliary port 24.

When the cylinder port 28 is located in the angle range where thecylinder port 28 is connected to the upper auxiliary port 23, and anentire stroke movement distance of the piston is regarded as 1, thestroke position of the piston 13 is in a position range of not less than0 and not more than about 0.008. When the cylinder port 28 is located inthe angle range where the cylinder port 28 is connected to the lowerauxiliary port 24, and the entire stroke movement distance of the pistonis regarded as 1, the stroke position of the piston is in a positionrange of not less than about 0.992 and not more than 1. When the piston13 is located at the dead center or the vicinity of the dead center, thestroke movement distance relative to a unit angle movement distance ofthe cylinder block 12 is small. Therefore, the angle range where thecylinder port 28 is connected to the auxiliary port 23 or 24 is about11% of one rotation (≈40°/360°), and the corresponding range of thestroke position of the piston 13 is about 1.6% (=about 0.008×2).

Further, in the present embodiment, the gradient of the change in thepressure P of the operating oil in the piston chamber 27 is made smallby the notch 90. Therefore, while the cylinder port 28 is connected tothe port 21, 22, 23, or 24 of the valve plate 11, the pressure P of theoperating oil in the piston chamber 27 does not always become constantpressure. For example, while the cylinder port 28 is connected to thehigh pressure side port that is the first or second port, the pressure Pdoes not always become the highest pressure P2. While the piston chamber27 is located in the vicinity of the angle position where the status ofconnection with the high pressure side port is switched betweenconnection and disconnection, that is, while the piston chamber 27 islocated in the vicinity of 10° or 170°, the pressure P graduallychanges.

In the oil-pressure motor 10, when the cylinder port 28 is located inthe angle range of more than 10° and less than 170° (10<θ<170), thepiston chamber 27 communicates with the supply/discharge port 21 that isthe high pressure side port, and pressure that is not less than averagepressure (P1+P2)/2 of the lowest pressure P1 and the highest pressure P2is introduced to the piston chamber 27. Further, when the cylinder port28 is located in the angle range other than the above, that is, when thecylinder port 28 is located in the angle range of not less than 0° andnot more than 10° (0≦θ≦10) or in the angle range of not less than 170°and less than 360° (170≦θ<360), the piston chamber 27 communicates withthe supply/discharge port 22 that is a low pressure side port, or theauxiliary port 23 or 24, and the pressure that is less than the averagepressure (P1+P2)/2 of the lowest pressure P1 and the highest pressure P2is introduced to the piston chamber 27.

Next, features of the oil-pressure motor 10 that is the liquid-pressurerotating device according to the present invention will be explained inmore detail. As shown in FIGS. 4 and 5, each of the supply/dischargeports (first and second ports) 21 and 22 is formed so as to face a routethrough which the base portion 67 of the cylinder port 28 passes whenthe cylinder block 12 rotates. It should be noted that each of thesupply/discharge ports 21 and 22 may be formed so as to face a routethrough which both the base portion 67 and convex portion 68 of thecylinder port 28 pass.

As shown in FIG. 4, each of the supply/discharge ports 21 and 22includes a wide portion 130, a narrow portion 131, and the notch 90.Inner peripheral edge sides 75 and 76 of the wide portions 130substantially coincide with the inner peripheral edge side 70 of themovement route of the cylinder port 28, and outer peripheral edge sides77 and 78 of the supply/discharge ports 21 and 22 substantially coincidewith the outer peripheral edge side 71 of the movement route of thecylinder port 28.

As shown in FIG. 4, the narrow portions 131 are formed at end portionsof the supply/discharge ports 21 and 22, the end portions being close toa top dead center switching land 132. Each of the narrow portions 131 isformed as a portion whose opening width W2 in the radial direction ofthe rotation of the cylinder block 12 is narrower than an opening widthW1 of the wide portion 130 in the same direction. To be specific, aninner peripheral edge side 131 a of the narrow portion 131 is formedoutside the inner peripheral edge side 70 of the movement route of thecylinder port 28 in the radial direction, and an outer peripheral edgeside 131 b of the narrow portion 131 substantially coincide with theouter peripheral edge side 71 of the movement route of the cylinder port28.

As shown in FIG. 4, each of the narrow portions 131 is formed in anangle range from a predetermined angle position (θ=0) in the top deadcenter switching land 132 where the piston 13 is located at the top deadcenter to an angle positon of not more than 55° (preferably) 45°) in therotational direction of the piston chamber 27. Further, the notches 90of the supply/discharge ports 21 and 22 are grooves.

As shown in FIGS. 4 and 5, each of the auxiliary ports 23 and 24 isformed so as to avoid a route through which the base portion 67 of thecylinder port 28 passes when the cylinder block 12 rotates and to face aroute through which the convex portion 68 passes when the cylinder block12 rotates. Inner peripheral edge sides 80 and 81 of the auxiliary ports23 and 24 coincide with an inner peripheral edge side of the movementroute of the convex portion 68 of the cylinder port 28. Each of outerperipheral edge sides 82 and 83 of the auxiliary ports 23 and 24 isformed at an inner side of the inner peripheral edge side 70 of themovement route of the base portion 67 of the cylinder port 28 in theradial direction by an interval W3.

To be specific, the base portion 67 of the cylinder port 28 is formedaway from each of the auxiliary ports 23 and 24 by a sealing portion 136having a predetermined seal width W3 (preferably not less than 3 mm) inthe radial direction.

As shown in FIGS. 4 and 5, the auxiliary ports 23 and 24 are formed suchthat when the piston chamber 27 located at the dead center of the valveplate 11 or the vicinity of the dead center does not communicate withthe high pressure side supply/discharge port 21 or 22, the auxiliaryport 23 or 24 communicates with this piston chamber 27.

Next, the actions of the oil-pressure motor 10 that is theliquid-pressure rotating device configured as above will be explained.As shown in FIG. 4, in the oil-pressure motor 10, portions of thesupply/discharge ports 21 and 22 which portions are located close to thetop dead center switching land 132 are formed as the narrow portions 131each of whose opening width W2 in the radial direction of the rotationof the cylinder block 12 is narrow. Therefore, in a state where thecylinder port 28 of the cylinder block 12 is not located so as tooverlap the narrow portion 131, a seal area between the rear end surface12 a of the cylinder block 12 and the valve plate 11 can be increased.With this, the amount of high-pressure operating oil leaking from thepiston chamber 27 through the supply/discharge port 21 or 22 can bereduced by a sealed region corresponding to the increased seal area.

The flow rate of the operating oil flowing through the portion (narrowportion 131) of each of the supply/discharge ports 21 and 22 whichportion is located close to the top dead center switching land 132 islower than the flow rate of the operating oil flowing through theportion (wide portion 130) of each of the supply/discharge ports 21 and22 which portion is far from the top dead center switching land 132.Therefore, even though the narrow portions 131 are formed as above, thepressure loss based on the flow of the operating oil can be preventedfrom increasing. The reason why the flow rate of the operating oilflowing through the portion close to the switching land 132 is low isbecause the movement speed of the piston 13 becomes slow as the piston13 gets close to the switching land 132 (see FIG. 6).

Similarly, the flow rate of the operating oil flowing through theportion of each of the supply/discharge ports 21 and 22 which portion islocated close to the bottom dead center switching land 133 is lower thanthe flow rate of the operating oil flowing through the portion of eachof the supply/discharge ports 21 and 22 which portion is far from thebottom dead center switching land 133.

Further, at the portion of each of the supply/discharge ports 21 and 22which portion is located far from the top dead center or bottom deadcenter switching land 132 or 133, the narrow portion 131 is not formed,but the wide portion 130 is formed. Therefore, the pressure loss basedon the flow of the operating oil flowing through the wide portion 130does not increase. With this, the volume efficiency of the oil-pressuremotor 10 can be effectively improved without deteriorating themechanical efficiency of the oil-pressure motor 10.

Then, as shown in FIG. 4, each of the narrow portions 131 is formed inan angle range from the predetermined angle position in the top deadcenter switching land 132 in which the piston 13 is located at the deadcenter to an angle position of not more than 55° (=θ2) in the rotationaldirection of the piston chamber 27. With this, the amount ofhigh-pressure operating oil leaking from the supply/discharge port 21 or22 through the sealed region between the rear end surface 12 a of thecylinder block 12 and the valve plate 11 shown in FIG. 2 can beeffectively reduced, and the increase in the pressure loss by the flowof the operating oil at the narrow portion 131 can be effectivelysuppressed.

It is preferable that the angle range where the narrow portion 131 isformed be an angle range of not more than 45° (=θ2). To be specific, themovement speed of the piston 13 can be calculated as a value whichchanges based on a sine function in which: a predetermined angleposition in the top dead center switching land 132 of the valve plate 11when the piston 13 is located at the top dead center is 0° (=θ); and therotation angle of the piston chamber 27 is 0 (see FIG. 6). The movementspeed of the piston 13 at the angle position where the rotation angle θof the piston chamber 27 is 45° is about 70% of the maximum movementspeed (the movement speed of the piston 13 becomes the maximum movementspeed when the piston 13 is located at the angle position where theangle θ is 90°. Each of the flow rate of the operating oil flowing intothe piston chamber 27 and the flow rate of the operating oil flowing outfrom the piston chamber 27 becomes about 70% of the maximum flow rate.Therefore, the opening width W2 of the narrow portion 131 in the radialdirection can be set to about 70% of the opening width W1 of the wideportion 130 of each of the supply/discharge ports 21 and 22, and thesealed region having an appropriate width can be formed.

Further, as shown in FIG. 5, the lower auxiliary port 24 is formed suchthat when the cylinder port 28 (piston chamber 27) located at the bottomdead center of the valve plate 11 or the vicinity of the bottom deadcenter does not communicate with, for example, the high pressure sidesupply/discharge port 21, the lower auxiliary port 24 communicates withthis cylinder port 28 (piston chamber 27). Similarly, the upperauxiliary port 23 is formed such that when the cylinder port 28 (pistonchamber 27) located at the top dead center of the valve plate 11 or thevicinity of the top dead center does not communicate with, for example,the high pressure side supply/discharge port 21, the upper auxiliaryport 23 communicates with this cylinder port 28 (piston chamber 27).

With this, when the cylinder port 28 of the piston chamber 27 performsthe rotational movement at the bottom dead center and the vicinity ofthe bottom dead center in a state where the cylinder port 28 of thepiston chamber 27 does not communicate with the high pressure sidesupply/discharge port 21 and is sealed by the valve plate 11, that is,in a state where the high-pressure operating oil is stored in thecylinder port 28 of the piston chamber 27, the lower auxiliary port 24communicates with the piston chamber 27, and the high-pressure operatingoil in the piston chamber 27 can be discharged through the lowerauxiliary port 24. Therefore, the high-pressure operating oil in thepiston chamber 27 can be prevented from leaking from between the rearend surface 12 a of the cylinder block 12 and the valve plate 11, andthe volume efficiency can be improved.

Further, with this, force applied from the piston 13 through the shoe 14to the swash plate 15 and force applied from the cylinder block 12 tothe valve plate 11 can be reduced, and frictional force between memberssliding each other, such as between the shoe 14 and the swash plate 15or between the valve plate 11 and the cylinder block 12, can be reduced.As a result, the mechanical loss can be reduced, and the seizeresistance between the members sliding each other improves, in otherwords, the seizing can be made hard to occur.

Then, as described above, by the reduction in the leak amount ofhigh-pressure operating oil, the oil-pressure motor 10 can be driven bypressure, lower than conventional pressure, at the time of start-up.

Further, when the cylinder port 28 shown in FIG. 5 performs therotational movement at the dead center of the valve plate 11 and thevicinity of the dead center, the base portion 67 of the cylinder port 28can be located away from each of the auxiliary ports 23 and 24 by thesealing portion 136 having the predetermined seal width W3 in the radialdirection. With this, in a state where the base portion 67 of thecylinder port 28 located at the dead center of the valve plate 11 or thevicinity of the dead center communicates with the high pressure sidesupply/discharge port 21, the high-pressure operating oil can beprevented from flowing out through the base portion 67 to the auxiliaryport 23 or 24. With this, the energy of the high-pressure operating oilcan be efficiently utilized.

Then, the convex portion 68 of the cylinder port 28 can be set so as tocommunicate with the auxiliary port 23 or 24 at a predetermined timingat which the base portion 67 of the cylinder port 28 shown in FIG. 5does not communicate with the high pressure side supply/discharge port21. With this, the high-pressure operating oil in the piston chamber 27communicating with the cylinder port 28 can be discharged through theauxiliary port 23 or 24.

Then, when the seal width W3 is not less than 3 mm, and the base portion67 of the cylinder port 28 at the dead center of the valve plate 11 orthe vicinity of the dead center communicates with the high pressure sidesupply/discharge port 21, the base portion 67 is located away from theauxiliary port 23 or 24 by the sealing portion 136 having the seal widthW3 of not less than 3 mm in the radial direction. Therefore, thehigh-pressure operating oil in the piston chamber 27 can be effectivelyprevented from leaking through the sealing portion 136 having the sealwidth of not less than 3 mm and flowing into the auxiliary port 23 or24.

Further, according to the oil-pressure motor 10, the piston chamber 27in the angle range where the piston 13 is located at the vicinity of thedead center can perform the supply and discharge of the operating oilthrough the auxiliary port 23 or 24. With this, the smooth movement ofthe piston 13 in the expanding direction and the contracting directionat the vicinity of the dead center can be achieved. In addition, theoperating oil having pressure higher than atmospheric pressure isintroduced to the auxiliary ports 23 and 24, and when the piston 13moves in the expanding direction at the vicinity of the dead center, itis unnecessary to suction the operating oil by negative pressuregenerated by the movement of the piston 13. Therefore, cavitation can beprevented.

Further, according to the oil-pressure motor 10, when the piston chamber27 stores the high-pressure operating oil without communicating with thehigh pressure side supply/discharge port 21 or 22 and performs therotational movement at the dead center and the vicinity of the deadcenter, the auxiliary port 23 or 24 can communicate with the pistonchamber 27, and therefore, the high-pressure operating oil in the pistonchamber 27 can be discharged through the auxiliary port 23 or 24.

In the above embodiment, as shown in FIG. 4, the narrow portion 131 isformed to have the opening width W2 that is substantially constant.However, instead of this, the narrow portion 131 may be formed such thatthe opening width W2 decreases as the narrow portion 131 extends towardthe top dead center of the valve plate 11.

To be specific, the flow rate of the operating oil in the piston chamber27 decreases as the piston chamber 27 moves toward the dead center(θ=0°) of the valve plate 11. Therefore, while suppressing the increasein the pressure loss based on the flow of the operating oil at thenarrow portion 131, the amount of high-pressure operating oil leakingfrom the supply/discharge port 21 or 22 through between the rear endsurface 12 a of the cylinder block 12 and the valve plate 11 can beefficiently reduced.

In the above embodiment, as shown in FIGS. 4 and 5, the auxiliary ports23 and 24 are through holes formed on the valve plate 11. However,instead of the through holes, as shown in FIGS. 8A and 8B, a concaveportion may be formed on an inner edge portion of an attachment hole 134formed at a middle of the valve plate 11, the rotating shaft 17 beingattached to the attachment hole 134. As with the above embodiment, thepressure of the operating oil introduced to this concave portion ismaintained higher than the atmospheric pressure and lower than thepressure ejected from the oil-pressure source and introduced to the highpressure side supply/discharge port 21 or 22. For example, the pressureof the operating oil introduced to the concave portion is maintained notless than 0.01 MPa and not more than 2 MPa. Other than this, the concaveportion is the same as the auxiliary ports 23 and 24 of the aboveembodiment, so that detailed explanations thereof are omitted.

Further, in the above embodiment, as shown in FIG. 1, the narrowportions 131 are formed at the respective upper end portions of thesupply/discharge ports 21 and 22. However, instead of this, the narrowportion 131 may be formed at any one of the lower end portions of thesupply/discharge ports 21 and 22.

Further, in the above embodiment, as shown in FIG. 1, the narrowportions 131 are formed at the respective portions of thesupply/discharge ports 21 and 22 which portions are located close to thetop dead center switching land 132, and the narrow portions 131 are notformed at the respective portions of the supply/discharge ports 21 and22 which portions are located close to the bottom dead center switchingland 133. However, instead of this, the narrow portions 131 may beformed at the portions of the supply/discharge ports 21 and 22 whichportions are located close to the top dead center switching land 132 andthe portions of the supply/discharge ports 21 and 22 which portions arelocated close to the bottom dead center switching land 133.

Further, in the above embodiment, as shown in FIGS. 4 and 5, the upperauxiliary port 23 and the lower auxiliary port 24 are provided. However,instead of these, only one of these auxiliary ports may be provided.

Further, in the above embodiment, as shown in FIG. 1, onesupply/discharge port 21 and one supply/discharge port 22 are providedat the left side and the right side, respectively. However, instead ofthese, as shown in FIG. 8A, a plurality of (three, for example)supply/discharge ports may be provided at each of the left and rightsides: In this case, the narrow portions 131 may be fanned at portslocated close to the top dead center switching land 132 among the threesupply/discharge ports 21 and the three supply/discharge ports 22.

Further, the above embodiment has explained an example in which theliquid-pressure rotating device of the present invention is used as avariable displacement swash plate type motor. However, instead of this,the liquid-pressure rotating device of the present invention can be usedas a variable displacement swash plate type pump or a fixed displacementmotor or pump.

Further, the liquid-pressure rotating device of the present inventioncan be used as each of a device that is rotatable in both normal andreverse directions and a device that rotates in only one direction.

In the above embodiment, the pressure of each of the auxiliary ports 23and 24 is set to be higher than the atmospheric pressure and lower thanthe pressure of the high pressure side supply/discharge port. However,instead of this, the pressure of each of the auxiliary ports 23 and 24may be set to become pressure of the drain tank by connecting theauxiliary ports 23 and 24 to the drain tank.

Further, the above embodiment has explained an example in which the oilis used as the operating liquid. However, instead of this, water may beused as the operating liquid.

Further, in the above embodiment, the notches 90 are included. However,the notches 90 may not be included.

From the foregoing explanation, many modifications and other embodimentsof the present invention are obvious to one skilled in the art.Therefore, the foregoing explanation should be interpreted only as anexample and is provided for the purpose of teaching the best mode forcarrying out the present invention to one skilled in the art. Thestructures and/or functional details may be substantially modifiedwithin the scope of the present invention.

INDUSTRIAL APPLICABILITY

As above, the liquid-pressure rotating device according to the presentinvention has excellent effect of being able to reduce the amount ofhigh-pressure operating oil leaking from the first or second portthrough the sealed region between the rear end surface of the cylinderblock and the valve plate and suppress the increase in the pressure lossof the operating oil flowing through the first and second ports. Thus,the present invention is suitably applied to such liquid-pressurerotating device.

REFERENCE SIGNS LIST

10 oil-pressure motor

11 valve plate

12 cylinder block

13 piston

14 shoe

15 swash plate

16 casing

17 rotating shaft

21 supply/discharge port (first port)

22 supply/discharge port (second port)

23 upper auxiliary port (third port)

24 lower auxiliary port (third port)

27 piston chamber

28 cylinder port

67 base portion

68 convex portion

90 notch

130 wide portion

131 narrow portion

131 a inner peripheral edge side

131 b outer peripheral edge side

132 top dead center switching land

133 bottom dead center switching land

134 attachment hole

136 sealing portion

137 drain port

L10 rotation axis

L11 tilt axis

W1 opening width of wide portion

W2 opening width of narrow portion

W3 seal width of sealing portion

1. A liquid-pressure rotating device comprising: a cylinder blockprovided rotatably and including a plurality of piston chambers formedat intervals in a circumferential direction; a plurality of pistonsfitted in the respective piston chambers so as to be movable in anexpanding direction and a contracting direction and configured toreciprocate in the expanding direction and the contracting direction;and a valve plate provided in contact with the cylinder block andincluding a first port, a second port, and a switching land formedbetween the first port and the second port, the first and second portscommunicating with the piston chambers, wherein: a portion of at leastone of the first and second ports of the valve plate which portion islocated close to the switching land is formed as a narrow portion havinga narrow opening width in a radial direction; an auxiliary port isformed at the switching land of the valve plate; pressure of theauxiliary port is maintained lower than pressure of a high pressure sideport that is any one of the first and second ports; and when the pistonchamber does not communicate with the high pressure side port that isthe first or second port, the piston chamber and the auxiliary portcommunicate with each other.
 2. The liquid-pressure rotating deviceaccording to claim 1, wherein the narrow portion is formed in an anglerange from a position of a dead center to a position of not more than45° in the circumferential direction.
 3. The liquid-pressure rotatingdevice according to claim 1, wherein: openings of the piston chamberswhich openings face the valve plate serve as cylinder ports; and theopening width of the narrow portion in the radial direction decreases asthe narrow portion extends toward the dead center.
 4. Theliquid-pressure rotating device according to claim 1, wherein: openingsof the piston chambers which openings face the valve plate serve ascylinder ports; each of the cylinder ports has a shape including a baseportion and a convex portion projecting from the base portion outward orinward in the radial direction; the convex portion is formed such thatwhen the piston chamber communicates with the auxiliary port through thecylinder port, only the convex portion communicates with the auxiliaryport; and before and after the piston chamber communicates with theauxiliary port through the cylinder port, the base portion is locatedaway from the auxiliary port by a sealing portion having a predeterminedseal width in the radial direction.
 5. The liquid-pressure rotatingdevice according to claim 4, wherein the seal width is not less than 3mm.